In the making of metal matrix composites (MMC's) comprising fine ceramic (e.g. alumina) reinforcement particles dispersed in a matrix comprising aluminum or its alloys, a semi-solid slurry (a thixotropic liquid/solid mixture) of the aluminum matrix material is formed in a refractory crucible, and the ceramic reinforcement particles are introduced into the aluminum slurry and mechanically mixed therein by a rotating mixing blade. Introduction of the ceramic reinforcement particles into the semi-solid aluminum slurry enables a high volume percentage, such as 30-40 volume %, of reinforcement particles to be dispersed in the aluminum matrix of the final MMC. Such an MMC process is described in the Flemings U.S. Pat. No. 3,948,650.
The mixing blade used to mechanically mix the ceramic reinforcement particles into the semi-solid aluminum slurry is subjected to tremendous abrasive action from the ceramic particles as they are dispersed in the semi-solid slurry. Expensive flame sprayed alumina coated stainless steel (Type 304) mixing blades used in the past typically exhibit catastrophic wear after only 30 minutes such that replacement with a new mixing blade is required.
There is a need for improved mixing blades for use in the manufacture of MMC's using semi-solid slurries as well in other manufacturing applications that process or handle molten or hot solid aluminum and its alloys.
An object of the present invention is to satisfy this need.